felony

N. A serious crime for which the punishment is prison for more than a year or death. Crimes of less gravity are called misdemeanours. This term is no longer used in England or other Commonwealth countries but remains a major distinction in the United States.

In California, "unlawful sexual intercourse" - statutory rape - is defined as sex between an adult and anyone under the age of 18 if the couple isn't married...If the age difference between the adult and the minor is more than three years, the crime may be a felony; if the difference is less, it's a misdemeanor.

You can find a detailed audio presentation of the difference in American law between felonies and misdemeanors here.